3 - Add your friends on the Steam client's instant messenger (you may skip this step if you don't have any friends).

4 - On the Steam client, click on Games > Add a Non-Steam Game to my Library.

5 - Browse to the Desktop folder and select the ET shortcut or browse to where you installed ET and select the program ET.EXE.

6 - On the Steam client, click on Library > Games. You should find ET listed there. Now, to standardize things, right click on the game's name on the list and select Properties, then edit the name so it shows Wolfenstein: Enemy Territory(there should be a space between the colon and the word Enemy).

7 - Still on ET's properties, you can set the command line parameters in the target field so they will be executed when the game is launched. Below is my command line to launch ET, which sets the memory values, changes the mod to Jaymod and connects to the [>NF<] ET Server automatically:

The part in RED is where I have ET installed, and it will probably be different to where you have it installed, so do not change that - just add the part in BLUE(if you happen to be color blind, ask for the assistance of a friend or family member).

8 - From now on, always launch ET from the Steam client, or everything you've done above will be have been useless. You can launch the game by double clicking on its name on the games list, right clicking on its name and selecting Launch, or clicking on the Steam icon in the system tray and selecting Wolfenstein: Enemy Territory.